Many of today's electronic systems require power supplies that can operate from higher system voltages. Examples include systems designed for automotive, industrial, and communications equipment whose operating input voltages can be 12V, 24V, or 48V and can vary over a wide range with transit spikes that can easily cause damage to the equipment.
Automotive electronics operate from the car battery which experiences transient loads such as cold-cranks and load dumps which can range from 5V to over 40V. In addition, technologies such as start-stop increase the transient range dropping down to 3V in certain case. This requires off-battery power ICs to withstand the harsh conditions and reliably provide power to the whole vehicle.
Some electronic devices, for example automotive cameras, utilized in the advanced driver assistance systems are fast growing. To support the operation of the automotive cameras, a typical automotive camera power solution includes a power over coax filter network, mid-VIN step-down DC-DC converter, and a low-VN power management IC (PMIC) are usually applied to efficiently supply voltages used for imagers and their accompanying serializers. For meeting the requirement of small solution size for easy installation and low thermal fluctuation by image sensor, integration of a multiple-output buck DC-DC converter as a PMIC is suitable for this application.
Multiple parallel DC-DC buck converter are most commonly used to generate multiple output voltages or currents. A conventional multiple-output buck converter consisting of two-stage power conversion is utilized. The conventional two stage multiple output buck converter is illustrated in FIG. 1. It can achieve high power efficiency through distributive voltage/current levels because of the inherent characteristics of the DC-to-DC buck converter. However, this topology requires four inductors (L1, L21, L22, and L23) for three outputs (VOUT1, VOUT2 and VOUT3), therefore larger form factor is induced.
A single-inductor multiple-output (SIMO) architecture provides a better solution for tiny devices requiring good thermal performance, by integrating functionality in smaller devices that would otherwise require multiple discrete components. As depicted in FIG. 2, a SIMO buck converter can support multiple output stages (VOUT1, VOUT2 and VOUT3) while using only one inductor (L1), its conversion efficiency is one stage efficiency and larger output voltage ripple can be reduced by low dropout regulators (LDOs) if required. The SIMO buck converters has many advantages over the conventional two-stage multiple-output converter, such as they benefits from small size, light weight and significant overall cost saving. Moreover, the dropout voltages of the LDOs can be respectively set to low enough (e.g. 50 mV˜100 mV) to optimize the power efficiency and finally the overall power efficiency can compete with the traditional two-stage configuration as FIG. 1 for many application conditions.
The concept of SIMO DC-DC converters arise in order to overcome the disadvantage of conventional converter such as complex and suffers from high cost, with multiple inductors and controllers required. The SIMO topology is capable of generating independently controlled buck, boost, and buck-boost outputs simultaneously. A control scheme is developed for reduced cross-regulation in SIMO DC-DC converters.
Since a SIMO converter can support multiple outputs while using only one inductor, it is an excellent candidate to minimize the component count and thus reduce the production cost. Apparently the area of print circuit board can be reduced greatly, thereby miniaturizing devices. However, the cross regulation of the SIMO converters suffer from instability in system dynamics due to coupled outputs. For a multiple-output converter with each output regulated independently, if one output is affected by the variation of other outputs, transient cross-regulation occurs. Therefore, minimizing the cross regulation is required in SIMO DC-DC converter design while improving the power delivery quality and the load driving capability are also important. For example, due to the demand increased power efficiency in PMICs, SIMO converter as the key device should be also operated under various load conditions, such as continuous current mode (CCM) in heavy load condition, discontinuous current mode (DCM) in light load condition, and pulse skipping mode in extreme light load or no load condition. To achieve these goals, a SIMO architecture with novel control scheme is still demanding.